X-ray fluorescence mapping of mercury on suspended mineral particles and diatoms in a contaminated freshwater system

Abstract

Abstract. Mercury (Hg) bioavailability and geochemical cycling is affected by its partitioning between the aqueous and particulate phases. We applied X-ray fluorescence (XRF) microprobes to directly visualize and quantify the spatial localization of Hg and its correlations with other elements of interest on suspended particles from a Hg contaminated freshwater system. Up to 175 μg g–1 Hg is found on suspended particles. Mercury is heterogeneously distributed among phytoplankton (e.g., diatoms) and mineral particles that are rich in iron oxides and natural organic matter (NOM), possibly as Hg-NOM-iron oxide ternary complexes. The diatom-bound Hg is mostly found on outer surfaces of the cells, suggesting passive sorption of inorganic Hg on diatoms. Our results indicate that localized sorption of Hg onto suspended particles, including diatoms and NOM-coated oxide minerals, is an important sink for Hg in natural aquatic environments.

Characteristics of dissolved organic matter (DOM) and relationship with dissolved mercury in Xiaoqing River-Laizhou Bay estuary, Bohai Sea, China

“…The Xiaoqing River-Laizhou Bay is influenced seasonally by desilting and flooding discharges from upstream, and thus the selective adsorption of Hg by SPM may be an important factor affecting Hg species mobility. Natural organic matter (NOM)-coated minerals may serve as the predominant sorption components of SPM for binding Hg through forming Hg-NOM complexes (Gu et al, 2014). Theoretically, the fractionation of DOM that occurs between solution (i.e., water) and solid (i.e., suspended particles) phases could results in adsorption of the aromatic component onto the minerals surfaces while leaving aliphatic compounds dissolved in the riverestuary.…”

Visualization of elemental distributions and local analysis of element-specific chemical states of an Arachnoidiscus sp. frustule using soft X-ray spectromicroscopy

“…These elements are the main constituents of diatom frustules composed of silica. Additionally, the SX-beam energy was tuned to be above the L 3 absorption edge to preferably excite calcium (Ca), which is considered a trace element originating from biological residues or present in the frustule as a bioincorporated mineral [ 18 , 21 , 25 ]. Two images were then recorded for each element at the excitation energies above or at the top of the resonance and below the absorption edge to generate a contrast-enhanced (CE) X-PEEM image.…”

“…However, since the invention of the electron microscope in the first half of the 20th century, many morphological studies have been conducted on diatoms, especially on the micro-/nanostructure of their frustules. Currently, to examine the micro-/nanostructural features of diatom frustules, various microscopic and spectromicroscopic methods, including optical microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) [3,[12][13][14][15][16][17][18][19][20][21], atomic force microscopy (AFM) [12,[14][15][16]19], transmission X-ray microscopy (TXM) [22,23], microprobe X-ray fluorescence (μXRF) analysis [24,25], and infrared (IR) microspectroscopy [3], are used to investigate diatoms.…”

“…Loic et al successfully elucidated that the silica wall typically consists of three overlapping porous layers, i.e., areola, cribrum and cribellum [12,14,15]. In the last decade, synchrotron radiation (SR)based μXRF analysis has been successfully applied to visualize the elemental distribution in diatom frustules [24,25]. In particular, de Jonge et al demonstrated that tomographic μXRF analysis has high potential to quantify the three-dimensional distributions of the elements in freshwater diatoms at 400 nm resolution [24].…”

“…e ., areola , cribrum and cribellum [ 12 , 14 , 15 ]. In the last decade, synchrotron radiation (SR)-based μXRF analysis has been successfully applied to visualize the elemental distribution in diatom frustules [ 24 , 25 ]. In particular, de Jonge et al .…”